What gives a microphone its sound has a lot to do with on-axis:off-axis interactions, something that you cannot apply after the fact (since the processor has no way of knowing the performer's position and micro-variations in front of the mics). You can capture the distortion and EQ curve of a mic but that doesn't really mimic the sound of that mic (and you'd probably be better off just applying the EQ and distortion to taste anyway).